This invention relates telecommunications trunk circuits and their relation to telecommunications switching systems.
Many modern switching systems carry out a plurality of functions such as local, toll, and local operator assistance. At the same time, the software for supporting each of these functions is maintained separately in order to allow features for each of these types of systems to be developed without requiring detailed studies of feature interactions among features of the different types of systems. Under these circumstances, it is frequently necessary for some types of calls, for example, calls between a local switch function and an operator service position system function to provide loop-around trunks in order to have a clean interface between the two types of calls. Under these circumstances an incoming call connection is established between an incoming trunk and one end of such a loop-around trunk, and a separate connection is established between the other end of the loop-around trunk and an outgoing trunk. The existence of a loop-around trunk ensures that the connection can be established within a switching system and the fact that the two connections are separate ensures that the features of one connection do not interfere with the features of the other connection. A problem of the prior art is that such loop-around trunks are expensive and must be generously engineered.
The above problem is solved and an advance is made over the prior art in accordance with Applicant""s invention wherein a first xe2x80x9cconnectionxe2x80x9d is established from the incoming trunk to a virtual loop-around trunk, i.e., a xe2x80x9ctrunkxe2x80x9d that exists only in memory, but has no physical appearance on the network, and a second xe2x80x9cconnectionxe2x80x9d is established from the other end of the virtual loop-around trunk to the outgoing trunk. After these xe2x80x9cconnectionsxe2x80x9d have been established a real connection is established directly from the incoming trunk to the outgoing trunk. Advantageously, this arrangement avoids the cost of a separate hardware loop-around trunk while retaining the independence of the software for the two xe2x80x9cconnections.xe2x80x9d
In accordance with one specific embodiment of Applicant""s invention, each connection is controlled by a pair of program processes (processes), one process for controlling each end of the connection. Four processes are involved in the type of connection discussed above. The processes associated with the virtual loop-around trunks communicate with the processes associated with the real trunk and return to these processes the same types of messages as would be returned if the connection were to a real loop-around trunk. As a last step, these two processes communicate with the processes for controlling the real trunks to establish the connection between the two real trunks.